This invention relates generally to diesel fuel control systems, and more particularly to diesel systems and methods for controlling hydrocarbon and diesel particulate matter levels in diesel exhaust emissions to assure safe environmental operation of diesel engines.
Internal combustion engines are designed to operate most efficiently on standard quality fuels, and the presence of impurities or non-combustible contaminants may result in poor engine performance or impairment as well as produce higher levels of exhaust impurities. It has been reported that even small quantities of water in diesel fuel may prevent satisfactory operation of a diesel engine, and most diesel engines now have some type of water-separator in addition to filters for removing sediment or other solids that may have been introduced into the fuel tank. It has also been reported that the presence of air entrained in diesel fuel delivered to a fuel injection system results in poorer engine performance since the amount of air required for optimum combustion is already precisely controlled by the fuel injection system itself. It is thus clear that the presence of these non-fuel contaminants in a diesel fuel delivery system results in poor engine performance with the extended result of less complete fuel burning and an increase in deleterious exhaust pollutants.
Most modern marine vessels with inboard engines have “wet exhaust” systems, wherein water is injected into the system to cool exhaust gases, and then passed overboard through the exhaust outlet. On a marine vessel with a water-cooled exhaust, the water in which the vessel floats (called “raw water”) cools both the engine and the exhaust. In the most common arrangement, a raw-water pump draws water from the engine intake seacock and through a strainer. It then pumps this water through a heat exchanger, and perhaps an oil cooler or two that are used to cool the engine, and then into the engine exhaust system, for example, via a water-injection nipple connected to a spray ring or mixing elbow in which the exhaust gases mix with the cooling water. The water then flows with the exhaust gases into a water silencer box, also called a water-lift box. The discharge pipe of the water-lift box is set slightly above the bottom of the box. The water level rises until it blocks the discharge pipe, at which point the trapped exhaust gases build up sufficient pressure to lift the water up the exhaust pipe and out of the boat, generally discharging the mix of water and exhaust gases through the hull, below the water line.
A wet exhaust has several advantages over a dry exhaust. The injected water lowers the temperature of the exhaust gases from as high as 2000° F. to below 212° F., cooling the gases sufficiently to allow the use of flexible hose at or shortly after the water injection point. Flexible hose is easier to run than pipe, is not subject to corrosion or stress cracking, and absorbs the movement and vibration of a flexibly mounted engine. The water-cooled exhaust needs no insulation, and does not pose a fire or burn hazard to either the boat or crew. What's more, as the temperature of the exhaust gases falls, the volume of the gases declines proportionately, reducing exhaust noise. At the same time, the minimal exhaust back pressure generally needed to lift the exhaust water out of the boat also muffles the sound.
During operation, diesel engines that are typical of marine vessels produce various exhaust pollutants, including unburned hydrocarbons, carbon oxides and nitrogen oxides, sulfurous gases and other particulate matter generally called “diesel particulate matter” (DPM). In particular, diesel exhaust systems of marine engines, such as diesel engines in yachts, can have adverse aesthetic effects and adverse environmental effects on marine ecosystems due to the discharge of pollutants such as hydrocarbons and DPM, which accumulate and agglomerate in marinas, on boat decks and hulls, and elsewhere. The particulates are solids, such as ash from lubricating oils, metal particles scraped from the cylinder walls, and dirt and dust that gets past the air filters. Current attempts to provide solutions to this problem include installing complex filtering systems and exhaust scrubbers. However, these solutions have various limitations due to factors such as complexity of the filter and scrubber systems and their high cost. Depending on the engine's mechanical condition, fuel and load, soot can make up 60 to 80 percent of the particulates. Aerosols, or ultrafine drops of water, fuel and other chemicals make up the remainder (R. Boggs, Dockwalk.com, October 2011, pp. 63-67).
Soot is an unavoidable byproduct of burning fuel oil in a diesel engine. Even when a diesel fuel is burning clean with no visible smoke, particulates still are a problem. This problem is most evident when vessels are docked or moored and diesel engine-driven electrical generators are being run for extended times and no forward velocity is available, so the DPM builds up in the water alongside the vessel. It has been reported that even a clear exhaust will foul the hull downwind with a swoop of yellow or black residue. Additionally, DPM collects on the surface of the water and nearby structures, including docks or other vessels. While a lesser problem, this is also true for the exhaust of diesel engines used for propulsion when the vessel is not underway or when maneuvering very slowly.
A perfectly operating 100 kW Tier 2-certified diesel engine driven generator, operating under optimum conditions, may legally discharge 720 grams (more than one and a half pounds) of particulates per day. This discharge, sometimes also referred to as “randomly agglomerated carbonaceous spherules,” is composed of particles that vary widely in size from around 4 μm (micron) down to 0.04 μm, with the majority of particles around 0.1 μm, which may explain how even invisible exhaust may contain a large amount of particulates that can bind with the surface of paint that appears to be as smooth and hard as glass.
It has been reported that installation of equipment for reduction of DPM on marine vessels has lagged far behind other industries because, until very recently, regulators considered the impact of marine air pollutants comparatively insignificant. The few exhaust emission regulations that applied to marine installations concentrated on major greenhouse gases such as oxides of sulfur and nitrogen. Particulate emissions from even the largest yachts remain essentially unregulated. The Engine International Air Pollution Prevention (EIAPP) certificate refers to NOx emissions from diesel engines that produce more than 130 kilowatts, not particulates, and until the International Maritime Organization (IMO) or port states impose limits or declare visible soot a marine pollutant, the problem is left to marina managers to decide how much soot is too much.
Systems that have been devised in the art to overcome some of the above problems are often quite complicated and costly, primarily involving elaborate filtering and scrubber systems. For example, US 2006/0021337, titled “Diesel Emissions Filtering System and Method,” discloses DPM reduction from diesel engine exhaust gases via passage of the gases through a scrubbing apparatus containing water and a low foaming wetting composition having high affinity for hydrocarbons. Likewise, U.S. Pat. No. 3,353,336, titled “Exhaust Gas Treatment Device,” discloses an exhaust gas treatment chamber comprising a plurality of compartments with angularly sloping baffles, a liquid recirculation system including a plurality of spray nozzles for dispersing liquid and a filter, and a chemical absorbent solution of borax, chlorophyll, trisodium phosphate and n-lauryl sulphate.
Accordingly, there is a need to develop new, practical, inexpensive solutions for facilitating eco-friendly dispersion, reduction or elimination of hydrocarbon, DPM and other pollutants from the exhaust gas emissions of diesel engines of marine vessels.